Accessibility Guide for colorblindness
According to WCAG 2 AAA contrast ratio thresholds, all text elements must have sufficient contrast between foreground text and background colors.
Some people with impaired eyesight have little contrast, meaning there are few bright or dark areas. Everything seems approximately the same brightness, making it difficult to detect outlines, borders, edges, and particulars. Text whose luminance (brightness) is too similar to the background can be difficult to read.
Nearly three times as many individuals suffer from low vision than total blindness. About 8% of males and 0.4% of women in the United States cannot see the typical complete spectrum of colors. A person with impaired vision or color blindness cannot distinguish text against an insufficiently contrasted background.
In the background, both color transparency and opacity are taken into account.
Transparency and opacity of colors in the foreground are more challenging to detect and account for due to:
- Background and foreground colors are same.
- Gradient backgrounds in CSS
- Background colors for pseudo-elements in CSS.
- Background colors generated using CSS borders.
- Overlap by another piece in the foreground - this can present positioning challenges.
- Elements shifted out of the viewport using CSS.
What this Accessibility Rule Checks
Examines each text element to check that the contrast between the foreground text and background colors meets the WCAG 2 AAA contrast ratio requirements.
This rule does not report text elements that have a background-image, are concealed by other components, or are text images.
This check additionally looks for child elements of disabled buttons so that they can be ignored to prevent a false value.
According to WCAG 2 AA contrast ratio thresholds, all text elements must have sufficient contrast between foreground text and background colors.
Some people with impaired eyesight have little contrast, meaning there are few bright or dark areas. Everything seems approximately the same brightness, making it difficult to detect outlines, borders, edges, and particulars. Text whose luminance (brightness) is too similar to the background can be difficult to read.
Nearly three times as many individuals suffer from low vision than total blindness. About 8% of males and 0.4% of women in the United States cannot see the typical complete spectrum of colors. A person with impaired vision or color blindness cannot distinguish text against an insufficiently contrasted background.
In the background, both color transparency and opacity are taken into account.
Transparency and opacity of colors in the foreground are more challenging to detect and account for due to:
- Background and foreground colors are same.
- Gradient backgrounds in CSS
- Background colors for pseudo-elements in CSS.
- Background colors generated using CSS borders.
- Overlap by another piece in the foreground - this can present positioning challenges.
- Elements shifted out of the viewport using CSS.
What this Accessibility Rule Checks
Examines each text element to check that the contrast between the foreground text and background colors meets the WCAG 2 AAA contrast ratio requirements.
This rule does not report text elements that have a background-image, are concealed by other components, or are text images.
This check additionally looks for child elements of disabled buttons so that they can be ignored to prevent a false value.
Notifies users of content that is hidden and unable to be checked for accessibility issues.
It is impossible to automatically check hidden content for accessibility rules breaches.
Screen reader users and sighted people must both be able to view visually hidden content. When content needs to be hidden from seeing users for a compelling reason, it is typically also necessary to hide it from blind users for the same reason. Making the content accessible to blind users makes sense when it is already available to sighted users.
When the CSS values display: none or visibility: hidden are used, content will be hidden from screen reader users (and all sighted users as well). The items become accessible to screen reader users when CSS properties are changed to display: block, display: inline, or other display values.
What this Accessibility Rule Checks
Checks for the presence of the hidden item content CSS style property values of display: none and visibility: hidden, and notifies users of their presence.
Makes sure that people who can’t differentiate colors can tell when text is a link by checking that the link has either a distinct style that doesn’t depend on color or a contrast difference of more than 3:1, which tells you that manual testing is needed.
Some people with low vision have low contrast, which means there aren’t many bright or dark areas. Everything looks about the same brightness, which makes it hard to see details, edges, borders, and outlines. It can be hard to read text that is the same brightness as the background.
There are almost three times as many people with low vision as there are who are totally blind. One in twelve people, or about 8% of men and 0.4% of women in the US, has a color deficiency. People with low vision or color blindness can’t tell what the text is against a background that doesn’t have enough contrast.
When there isn’t a 3:1 color contrast between the color of the link text and the color of the text around it, people with low vision or low contrast can’t tell by looking that the text is meant to be a link.
What this Accessibility Rule Checks
Checks that all links in blocks of text have a color difference of at least 3:1 from the text around them, so that people who can’t tell the colors apart can still find the link.
This rule looks at some of the most common ways to tell a link from the text around it, such as underlining, font styling, a border, or a background. No rule has been broken if the link has its own style that doesn’t depend on color (pass). There is a violation if the link doesn’t have a clear style and the contrast is less than 3:1. (fail). When the link doesn’t have a distinct style and the contrast difference is 3:1 or higher, you must check that the link has a distinct style when you focus on it or hover over it. This can’t be reliably done by a computer, so you have to do it by hand.